Method preflight

/**
 * Function called before extension installation/update/removal procedure commences
 *
 * @param   string            $type    The type of change (install, update or discover_install, not uninstall)
 * @param   InstallerAdapter  $parent  The class calling this method
 *
 * @return  boolean  True on success
 *
 * @since   3.6
 */
public function preflight($type, $parent)
{
    // Check for the minimum PHP version before continuing
    if (!empty($this->minimumPhp) && version_compare(PHP_VERSION, $this->minimumPhp, '<')) {
        Log::add(Text::sprintf('JLIB_INSTALLER_MINIMUM_PHP', $this->minimumPhp), Log::WARNING, 'jerror');
        return false;
    }
    // Check for the minimum Joomla version before continuing
    if (!empty($this->minimumJoomla) && version_compare(JVERSION, $this->minimumJoomla, '<')) {
        Log::add(Text::sprintf('JLIB_INSTALLER_MINIMUM_JOOMLA', $this->minimumJoomla), Log::WARNING, 'jerror');
        return false;
    }
    // Extension manifest file version
    $this->extension = $parent->getName();
    $this->release = $parent->getManifest()->version;
    $extensionType = substr($this->extension, 0, 3);
    // Modules parameters are located in the module table - else in the extension table
    if ($extensionType === 'mod') {
        $this->paramTable = '#__modules';
    } else {
        $this->paramTable = '#__extensions';
    }
    // Abort if the extension being installed is not newer than the currently installed version
    if (!$this->allowDowngrades && strtolower($type) === 'update') {
        $manifest = $this->getItemArray('manifest_cache', '#__extensions', 'element', $this->extension);
        // Check whether we have an old release installed and skip this check when this here is the initial install.
        if (!isset($manifest['version'])) {
            return true;
        }
        $oldRelease = $manifest['version'];
        if (version_compare($this->release, $oldRelease, '<')) {
            Factory::getApplication()->enqueueMessage(Text::sprintf('JLIB_INSTALLER_INCORRECT_SEQUENCE', $oldRelease, $this->release), 'error');
            return false;
        }
    }
    return true;
}